1. Field of the Invention
This invention relates to an automatic instrument adapted to detect microorganisms in a culture media and by means of measurement of the level of gaseous products, evaluate these media. This measurement is achieved without the need for extraction of the product.
2. Description of the Prior Art
The measurement of bacterial microorganisms has been addressed in many issued patents, among which are: Pat. No. 3,941,660 to MIRSKY as issued March 2, 1976. This patent refers to the use of radioactive material which generates radioactive CO.sub.2 in metabolism, which Applicant's invention is specifically intended to eliminate because of the legal restrictions involved in handling radioactive materials. In particular, this detection system uses sharp instruments or needles which must be inserted through the vial septums, with the likelihood of clogging, and the need to alter vial orientation to maintain septum integrity. Applicant's invention, hereinafter detailed and claimed, is a non-invasive method for measuring gas concentration in sealed containers subject to agitation of the liquid contained in the containers.
Also of note is BRUCE et al, (U.S. Pat. No. 3,963,927) as issued June 15, 1976. This patent shows apparatus for measuring the increase in concentration of CO.sub.2 generated by insect respiration which is allowed to build up in a sample cell to a degree sufficient to be measured by a Luft-type infrared CO.sub.2 gas analyzer.
Also of note is WATERS (U.S. Pat. No. 3,997,404) as issued December 14, 1976. This patent shows an apparatus and method which describes measurement of radioactive CO.sub.2 generated by bacterial metabolism through gas-tight cells having a light-permeable wall section, although infrared is not employed, rather scintillation counting. Also noted was WEAVER (U.S. Pat. No. 4,197,369) as issued April 8, 1980. This patent describes the use of a permeable membrane and means for measuring directly the amount of vaporous product passing through the membrane through the use of a mass spectrometer. While a membrane does provide a gas-liquid separation means, using the teaching of WEAVER the membrane would be subject to clogging by turbid liquids which would impede gas transport and so is not useful as a low-cost, commercial instrument where sample vials pass through a number of hands, with attendant turbulence before measurements are made.
Also noted is WADE (U.S. Pat. No. 4,250,266) as issued February 10, 1981, which provides apparatus such as the use of a carousel mentioning a "fully automated incubation and detection system," including a closed incubated chamber including agitation of culture bottles and indexing of trays, with the periodic measurement of the electrical parameters of the contents of each bottle with the display and results, all controlled by a microprocessor. The method of measurement of bacterial growth in WADE includes measurement of electrical conductivity, i.e., the magnitude of the voltage measured when a current is passed through the fluid. This measurement is of the growth of the microorganisms in the culture. Physical changes in the culture can affect electrical conductivity, whereas the generation of CO.sub.2 is prima facie evidence of actual bacterial metabolism.